permeation basics and their importance for the packaging industry · 2019. 12. 2. · dr. adolf...
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Permeation basics and their
importance for the packaging industry
Mr. Gabriele Benedetti, MSc
Area Sales Manager Europe - Permeation Testing Systems
MOCON, Business Unit of AMETEK
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MOCON
Market leader for Permeation Testing Analyzers since 1963
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Ingress / Egress
Scalping
Shelf Life
Flavor Loss
Oxygen
Water Vapor
WHY IS PERMEATION IMPORTANT?
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THE BALANCE BEETWEN FOOD AND PACKAGING WASTE
Minimum environmental impact
Minimum
material
OPTIMUM
PACK DESIGN
Increasing packaging
material weight or volume
Negative
environmental
impact
Overpackaging Underpackaging
Packaging waste
Food waste
Ultimately,
the customer
decides
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Micro and macroscopic cracks
(d>1 µm)
Pinholes, pores and
microchannels (2 nm<d<1 µm)
Inter and intra-molecular
spaces
CIN <<< COUT
CAPILLARY FLOWS
ACTIVE DIFFUSION
PERMEATION OR DIFFUSION?
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Dr. Adolf Eugen Fick
𝑭 = −𝑫𝝏𝑪
𝝏𝒙
WHAT IS PERMEATION?
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Permeation rate
Transmission rate
𝒄𝒎𝟑 ∙ 𝒄𝒎
𝒎𝟐 ∙ 𝒅𝒂𝒚 ∙ 𝒂𝒕𝒎
𝒄𝒎𝟑
𝒎𝟐 ∙ 𝒅𝒂𝒚
PERMEATION BASICS
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Steady State
Transient
p2 p1
C1 C2 𝑸 =
𝑨 ∙ 𝒕 ∙ 𝑫 ∙ 𝑪𝟏 − 𝑪𝟐
𝒍
l
𝑸 =𝑨 ∙ 𝒕 ∙ 𝑫 ∙ 𝑺 ∙ 𝒑𝟏 − 𝒑𝟐
𝒍
Q = quantity of permeant transferred
through the material
A = area of the sample
t = time
D = Diffusion coefficient
C = permeant concentration
l = thickness
𝑪 = 𝑺 ∙ 𝒑
S = Solubility coefficient
p = gas partial pressure
SOLUTION-DIFFUSION MECHANISM
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0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 2 4 6 8 10 12 14
No
rmal
ize
d F
lux
F/F ∞
1/X = 4Dt/l2
THEORETICAL PERMEATION CURVE
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Top of cell
Bottom of
cell
Flush Gas In Flush Gas Out
Test Gas In Test Gas Out
Carrier Gas In Carrier Gas + Test Gas
Out to sensor
Film test sample
O-rings
Flush channel
0
𝑱 = 𝑫𝑪𝟏 − 𝑪𝟐
𝒙
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SPERIMENTAL PERMEATION CURVE
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,5 1 1,5 2
No
rmal
ize
d F
lux
F/F ∞
1/X = 4Dt/l2
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,5 1 1,5 2 2,5 3
No
rmal
ize
d F
lux
F/F ∞
1/X = (4D/l2)t
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
No
rmal
ize
d F
lux
F/F ∞
1/X = (4D/l2)t
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 1 2 3 4 5 6 7
No
rmal
ize
d F
lux
F/F ∞
1/X = (4D/l2)t
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 1 2 3 4 5 6 7 8 9
No
rmal
ize
d F
lux
F/F ∞
1/X = (4D/l2)t
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 2 4 6 8 10
No
rmal
ize
d F
lux
F/F ∞
1/X = (4D/l2)t
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 2 4 6 8 10 12
No
rmal
ize
d F
lux
F/F ∞
1/X = (4D/l2)t
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 2 4 6 8 10 12 14
No
rmal
ize
d F
lux
F/F ∞
1/X = 4Dt/l2
THEORETICAL PERMEATION CURVE
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POLYMER CHARACTERISTICS
Atomic structure, Density, Crystallinity, Molecular
weight, Glass transition, Crosslinking
ENVIROMENTAL CONDITIONS
Relative humidity, Total pressure, Difference of partial
pressure, Temperature, Kind of gas
TECHNOLOGIC FACTORS
Plasticizers, Fillers, Residual solvents, Orientation,
Polymer blend, Copolymers and Composite
structures, Surface, Thickness
FACTORS AFFECTING PERMEATION
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PERMEATION IS IMPACTED BY
MATERIAL PROPERTIES
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CHEMICAL ADDITIONS TO POLYMER
BACKBONE
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CRYSTALLINITY
15 x 15 micron AFM image showing
nucleus and lamellar crystallites.
The partial crystallization of the material modifies both the free
volume (i.e. Solubility S0) and the frequency of the molecular
motions (i.e. Diffusion Coefficient D) and therefore also the
permeability coefficient P
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• The degree of packing, crystallinity, and orientation of the molecular
chains affect barrier properties
• Close packing and/or high crystallinity results in low free volume
and better barrier.
• Orientation results in better barrier by creating a more tortuous
diffusion path.
POLYMER MORPHOLOGY O2
PERMEATION* COMMENTS
PET (poly(ethylene terephlate)) 10% crystalline 10.0
PET 50% crystalline 5.0 Higher crystallinity reduces the available sites for permeation
PET 50% crystalline and oriented
3.0
Crystallinity and orientation produces more tortuous path for permeation
* cm3∙mil/(100 in2∙day∙atm)
CRYSTALLINITY
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AGING
Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)
Variation of the
oxygen permeation
with the aging time
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Effect of permeant size: diffusion rate decreases
as permeant size increases.
Molecule Diameter (nm) Molecule Diameter (nm)
𝑯𝒆 0.26 𝑪𝟐𝑯𝟒 0.39
𝑯𝟐 0.289 𝑿𝒆 0.396
𝑵𝑶 0.317 𝑪𝟑𝑯𝟖 0.43
𝑪𝑶𝟐 0.33 𝒏 − 𝑪𝟒𝑯𝟏𝟎 0.43
𝑨𝒓 0.34 𝑪𝑭𝟐𝑪𝒍𝟐 0.44
𝑶𝟐 0.346 𝑪𝟑𝑯𝟔 0.45
𝑵𝟐 0.364 𝑪𝑭𝟒 0.47
𝑪𝑶 0.376 𝒊 − 𝑪𝟒𝑯𝟏𝟎 0.50
𝑪𝑯𝟒 0.38
GAS SELECTIVITY
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PERMEATION IS IMPACTED BY
ENVIRONMENTAL CONDITIONS
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ENVIRONMENTAL EXPOSURE
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TEMPERATURE
LDPE d=50 µm
Time (sec)
Perm
eab
ilit
y (
cm
3/(
m2∙d
ay∙b
ar)
TRANSIENT
STEADY STATE
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TEMPERATURE
0
100
200
300
400
500
600
0 50 100 150 200
WV
TR
(m
g/(
m2∙d
ay)
Time (h)
WVTR at different temperatures
85°C
50°C
23°C
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TEMPERATURE
• Permeation rates typically change 5-7% per degree C
• For every 10°C increase in temperature, Transmission Rate doubles
• Crucial errors can occur when testing at elevated temperatures close to Tg.
• Package testing is of special concern due to temperature variations in ovens.
Gas T
ran
sm
issio
n R
ate
Temperature
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EFFECTS OF HUMIDITY ON OTR
Polymer 0%RH 100%RH
*K. Cooksey, IMPORTANT FACTORS FOR SELECTING FOOD PACKAGING MATERIALS BASED ON PERMEABILITY
(10∙1011 ml∙cm/(cm2∙sec∙cmHg ) analyzed at 25°C
Nylon 6 0.06 0.3
PVA 3.3 9.0
ABS 0.06 0.06
HDPE 6.6 6.6
LDPE 28.8 28.8
PVOH 0.0006 1.5
Uncoated Cellophane
0.0078 12.0
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EFFECTS OF HUMIDITY ON OTR
0,001
0,01
0,1
1
10
0 20 40 60 80 100
O2 P
erm
ea
tio
n
(cm
3∙m
il/(
100
in2∙d
ay∙a
tm)
RH (%)
NYLON 6 @ 23°C
SELAR® PA @ 23°C
NYLON MXD6 @ 23°C
44% EVOH @ 20°C
30% EVOH @ 20°C
SELAR® OH PLUS @ 23°C
*Web Coating & Handling Conference 2014 Europe, 10 June 2014
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PERMEATION IS IMPACTED BY
TECHNOLOGIC FACTORS
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ADDITIVES
PVC Poly (vinyl chloride)
Material state Pure, rigid
PVC Plasticized,
soft PVC O2 Permeation rate (cm3∙mil)/(100in2∙day∙atm)
8 150
• Additives used in manufacturing or in modifying the
polymer can affect permeation.
• Depending on the upon the chemical nature, as well
as the manner which the additive is blended, the
barrier can be either enhanced or reduced.
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SURFACE EFFECT
• The nature of the surface can determine the permeability as much as the polymer bulk.
• An example is hydrocarbon permeation through polyethylene:
– Polyethylene polymer is very nonpolar and thus a very poor barrier to nonpolar permeants such as hydrocarbon liquids.
– By treating the surface with fluorine gas, the fluorine adds on to the chains at or near the surface and by virtue of its bulk and polarity prevents hydrocarbon liquids from entering the polymer
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MATERIAL THICKNESS
Thinner samples = higher transmission
rates
When thickness is doubled, it takes 4X
longer to reach equilibrium
𝑮𝑻𝑹 ∝𝟏
𝒍
𝒕 = 𝒍𝟐
𝟔𝑫
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IMPORTANCE OF TESTING WHOLE
PACKAGE
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TESTING THE WHOLE PACKAGE
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TESTING THE WHOLE PACKAGE
[O2](g) 20.9% (room air) 100%
OTR
Equilibrium Time
[O2](g) 20.9% (room air) 100%
OTR 0.0012 cm3/(pkg∙day) 0.0052 cm3/(pkg∙day)
Equilibrium Time
[O2](g) 20.9% (room air) 100%
OTR 0.0012 cm3/(pkg∙day) 0.0052 cm3/(pkg∙day)
Equilibrium Time 4 days 4 days
𝑭 = −𝑫𝝏𝑪
𝝏𝒙
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CASE STUDIES
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COOKIE PACKAGE CASE STUDY
Ship to Film A
(Excellent)
Film B
(Good)
Film C
(Fair)
Testing
Conditions
Northern
Europe PASS PASS PASS
15°C
30% RH
South
Korea PASS PASS FAIL
23°C
50%RH
Vietnam PASS FAIL FAIL 30°C
85%RH
Apply average destination environmental conditions to test
conditions
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FAILED HAM PACKAGE CASE STUDY
• Ready-to-eat ham
• Packed in clear film pouch
• Ham spoiled before anticipated shelf life
• Packaging film delaminated
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Ham product
• Measured 75% RH in headspace
Packaging Material
• PE/Nylon/sealing layer
OTR
• Vendor tested: 0.05 cm3/(pkg·24h) at 4°C and 0%RH
• MOCON tested: 0.4 cm3/(pkg·24h) at 4°C and 75% RH
FAILED HAM PACKAGE CASE STUDY
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HEALTH SUPPLEMENT PACKAGING
CASE STUDY
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Sample WVTR (g/(pkg·day))
W-1 0.0070
W-2 0.0089
W-3 0.0099
W-4 0.0042
W-5 0.0107
W-6
(no cap) 0.003
0
0,002
0,004
0,006
0,008
0,01
0,012
W-1 W-2 W-3 W-4 W-5 W-6 (no cap)
WV
TR
(g
/(p
kg
·da
y))
Different liner in W-1 to W-5
Bottle WVTR results
HEALTH SUPPLEMENT PACKAGING
CASE STUDY
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INFANT FORMULA CASE STUDY
From metal can to flexible pouch
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INFANT FORMULA CASE STUDY
ID WVTR Film
g/(m2·day)
A <0.005
B <0.005
C <0.005
D <0.005
E <0.005
WVTR Package
g/(pkg·day)
0.0021 (met)
0.0010 (foil)
0.0022 (met)
0.0034 (met)
0.0015 (foil)
Pouch test results (23°C, 100%RH)
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TARGET SHELF LIFE (BALANCE)
• Target shelf life
of 300 days
• Product fails at
0.7 total grams
of moisture
ID WVTR Package
g/(pkg·day)
Total Days
Shelf Life
B 0.0010 700 days
A 0.0021 333 days
D 0.0034 205 days
Over
Packaging
700 days
Under
Packaging
205 days
Target
Packaging
333 days
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